Push-to-talk over cellular (PoC), also referred to as “direct connect” is a service which permits a user or transmitter to transfer a voice message to one or more receivers simultaneously via a mobile telephone interface. Within the scope of a PoC communication, the voice data is usually already distributed over the mobile telephone communications network, i.e. transferred to the desired receiver or receivers, as the voice signal to be transmitted is spoken into the mobile telephone terminal by the user. A PoC communication corresponds to the CB radio but is extended in such a way that the transmitter can speak to receivers throughout the world, which can be reached via the suitable switching technology of at least one mobile telephone communications network.
The following publications are cited in this document:
[1] Push to talk-over-Cellular (PoC); Architecture V1.1.0, Technical specification (2003-08);
[2] RFC 3261, SIP: Session Initiation Protocol, 2002.
[1] describes an industrial specification of a consortium of companies, in which, inter alia, Nokia, Ericsson, Motorola and Siemens are involved, based on the PS domain (i.e. packet-switched domain).
[1] describes two different variants for setting up a push-to-talk communications link (i.e. a PoC session) which differ in terms of the time at which a first PoC user can begin to talk to a PoC server unit after the push-to-talk communications link has been set up, i.e. after a PoC session has been set up, and the voice signals which are spoken into the device are transmitted to the at least one second, selected PoC user.
According to a first variant described in [1], which is referred to as a Late Media Mode (also referred to as Confirmed Indication Mode), an enable signal is not transmitted to the first PoC user, i.e. a first PoC client unit, in order to transmit useful data, preferably useful voice data, until a push-to-talk communications link has actually been set up to the selected at least one second PoC user, i.e. to the at least one second PoC client unit to which a PoC communications link is to be set up, and the at least one second PoC user has also accepted the PoC call.
In this case, only then is the respective voice message transferred from the first push-to-talk client unit to the second push-to-talk client unit.
FIG. 2 shows, in a message flow chart 200, the exchange of SIP messages (Session Initiation Protocol) which, in order to set up a PoC communications link in the confirmed indication mode, are exchanged between a first PoC client unit 201—implemented in a mobile telephone terminal—an IMS core communications network 202 (Internet Protocol Multimedia Subsystem) and a PoC server unit 203. According to the message flowchart 200 it is assumed that the PoC server unit 203 is operated in the late media mode.
If a request to set up a push-to-talk communications link to at least a second PoC client unit is entered into at least one second PoC client unit by means of a communications link setup request 204 by a user of the mobile telephone terminal in which the first PoC client unit 201 is implemented, a first SIP-INVITE message 205 according to the Session Initiation Protocol (SIP) such as is described, for example, in [2] is transferred to the IP Multimedia Subsystem (IMS) core communications network 202 from the first PoC client unit 201. If the IMS core communications network 202 receives the SIP-INVITE message 205, the IMS core communications network 202 of the first PoC client unit 201 confirms the attempt at setting up a communications link by means of a SIP-100 trying message 206. In addition, the IMS core communications network 202 passes on the SIP-INVITE message 205 to the PoC server unit 203. The PoC server unit 203 also acknowledges the reception of the SIP-INVITE message 205 with a SIP-100 trying message 207 which it transfers to the IMS core communications network 202.
Optionally, within the scope of the setup of the communications link it is possible to transfer a call signal message, encoded as a SIP-180 ringing message 208, from the PoC server unit 203 to the IMS core communications network 202 and from there to the first PoC client unit 201.
If a communications link has been successfully set up from the PoC server unit 203 to the at least one selected, i.e. desired, second PoC client unit (not shown in FIG. 2), the PoC server unit 203 transfers an enable message in the form of a SIP-200-OK (INVITE) message 209 to the IMS core communications network 202 and by means of the latter to the first PoC client unit 201 which itself outputs a communications setup indication 210 to the user of the mobile telephone terminal. The first PoC client unit 201 can then begin to transmit useful data, in particular to transmit voice data spoken into the PoC server unit 203 by the user, and via the latter to the at least one second PoC client unit.
In addition, an acknowledgement message in the form of a SIP-ACK message 211 is transmitted to the IMS core communications network 202 and via the latter to the PoC server unit 203 from the first PoC client unit 201.
Then, after the push-to-talk server unit 203 has received the acknowledgement message 211, the latter transmits a subscriber notification message as a SIP-NOTIFY message 212 to the IMS core communications network 202 which passes the SIP-NOTIFY message 212 on to the first PoC client unit 201. After the reception of the SIP-NOTIFY message 212 by the first PoC client unit 201, a communication setup confirmation message 213 in the form of a SIP-200-OK message 213 is transferred to the IMS core communications network 202, and from the latter to the PoC server unit 203, by which means the communications link is set up, as a termination of the setup of a push-to-talk communications link between the first PoC client unit 201 and the at least one selected second PoC client unit.
According to the second variant, which is referred to as an early media mode (also referred to as unconfirmed indication mode), an enable signal for the transmission of useful data, in particular for the transmission of spoken-in voice signals, is already fed to the first PoC client unit 201 if the PoC communications link is present between the first PoC client unit 201 and the PoC server unit 203 although a complete PoC communications link has not yet been set up to the selected second PoC client unit or units.
In other words, according to the second variant the user of the first PoC client unit 201 can already start to talk and the voice data is already transmitted even though the “selected” client, i.e. the “selected” second PoC client unit or units have not yet been reached by the PoC server unit 203.
All that is required according to this mode is that the selected second PoC client unit or units are signed on in the mobile telephone communications network or to the PoC service, in other words are on line, and the respective user of the selected second PoC client unit has set what is referred to as the “automatic answering mode”, when a PoC communications link setup message is received by means of the PoC server unit 203. The term “automatic answering mode” refers to a mode in which the received voice message is output without interaction with the receiver of a PoC voice message at his respective terminal, and he therefore does not need to explicitly “accept” an incoming call. In this mode, the voice messages are buffered in the PoC server unit and only transferred to the respectively selected second PoC client unit as soon as said unit has been reached.
FIG. 3 is a message flowchart 300 showing the flow of messages between the first PoC client unit 201, the IMS core communications network 202 and the PoC server unit 203 for a situation in which the PoC server unit 203 is operated in the early media mode, i.e. in the unconfirmed indication mode.
In response to the inputting of a communications link setup request 301 by a user into the mobile telephone terminal in which the first PoC client unit 201 is implemented, the first PoC client unit 201 transfers a first SIP-INVITE message 202 to the IMS core communications network 202 in accordance with the SIP.
If the IMS core communications unit 202 receives the SIP-INVITE message 302, the IMS core communications network 202 transfers a first confirmation message 303 as a SIP-100 trying message 303 to the first PoC client unit 201 in response to the reception. In addition, the IMS core communications unit 202 passes on the SIP-INVITE message 302 to the PoC server unit 203 which itself transfers a communications link accepted message 304 as a SIP-202 accepted message 304 to the IMS core communications network 202. The IMS core communications network 202 passes on this message to the first PoC client unit 201. After the first PoC client unit 201 has received the SIP-202 accepted message 304, it outputs a communications link indication 305 to the user of the first PoC client unit 201. In addition, the first PoC client unit 201 transfers a confirmation message 306 as a SIP-ACK message 306 to the IMS core communications network 202 which passes this on to the PoC server unit 203.
Once the first PoC client unit 201 has received the SIP-202 accepted message 304, the voice signals which have been spoken in by the user are transmitted from the first PoC client unit 201 to the IMS core communications network 202 and via it to the PoC server unit and buffered there.
If a communications link is set up to the at least one second, i.e. selected PoC client unit (not shown in FIG. 3), the PoC server unit 203 transmits a subscriber confirmation message 307 in the form of a SIP-NOTIFY message 307 to the IMS core communications network 202 which, for its part, transfers it to the first PoC client unit 201.
After reception of the SIP-NOTIFY message 307, the first PoC client unit 201 outputs an indication 308 that the communications link has been set up to the user, which indication specifies that a communications link has actually been set up to the selected second PoC client unit or units.
The first PoC client unit 201 then transfers a communications link setup confirmation message 309 as a SIP-200-OK (NOTIFY) message 309 to the IMS core communications network 202 which, for its part, passes on the message to the PoC server unit 203.
According to the current standardization efforts there is provision for the PoC server unit to have to support the confirmed indication mode but only to have to support the unconfirmed indication mode on an optional basis. If a PoC server unit supports both the confirmed indication mode and the unconfirmed indication mode, it can select, at each setup of a PoC communications link, i.e. at each setup of a PoC session, which of the two modes is offered to the respective PoC user. In addition, the PoC user who sets up a PoC session, i.e. initiates it, is also to be able to select whether he would like to use the unconfirmed indication mode (if the PoC server unit supports this) or in any case would like to use the confirmed indication mode.
According to [1], in the case in which the PoC server unit is operated in the confirmed indication mode, it is irrelevant which mode the user of the respective PoC client unit would like to use.
The confirmed indication mode is always used by the PoC server unit, and thus for the entire PoC communications link, i.e. as soon as the communications link has been set up to the at least one “selected” second PoC client unit and the latter has accepted the incoming call, the PoC server unit 203 transmits the SIP-200-OK (INVITE) message 209 which is described above to the first PoC client unit 201.
After the SIP-200-OK message 209 has been received, the user of the first PoC client unit 201 can start to speak and the speech signals which are spoken in are transmitted from this time to the IMS core communications network 202 and passed on from there directly to the selected second PoC client unit or units.
If, as illustrated in FIG. 3, the PoC server unit 203 is operated in the unconfirmed indication mode, the communications link between the first PoC client unit 201 and the PoC server unit 203 is set up when the transfer takes place, i.e. when the SIP-202 accepted message 304 is received in the first PoC client unit 201.
In this case, two situations can be distinguished from one another.
If the user of the first PoC client unit 201 would like to use the unconfirmed indication mode, he can start to speak after reception of the SIP-202 accepted message 304, and the spoken-in voice signals are transmitted from the first PoC client unit 201 to the IMS core communications unit 202 and from there to the PoC server unit 203. As a result the unconfirmed indication mode is used.
However, if the user of the first PoC client unit 201 would like to use the confirmed indication mode, he does not consider the reception of the SIP-202 accepted message 304 as a confirmation that he can start to transfer voice data but rather he waits until the first PoC client unit 201 informs him, with the reception of the SIP-NOTIFY message 307 by means of the communication setup confirmation indication 308, that the communications link has been set up to the “selected” second PoC client unit or units and the user of the respective second PoC client unit has accepted the PoC call. The user of the first PoC client unit 201 can then start to speak and the spoken-in voice signals are transmitted to the IMS core communications network 202 and from there by means of the PoC server unit 203 to the selected second PoC client unit or units. As a result, in this case the confirmed indication mode is used.
Generally, according to [1] it is generally provided that, with the first SIP-INVITE message 205 or 302 which is transmitted by the first PoC client unit 201, a SIP-SUBSCRIBE is implicitly actuated, on the basis of which the PoC server unit transmits a SIP-NOTIFY message to the first PoC client unit 201 each time as soon as a selected second PoC client unit has accepted the call.
However, within the scope of the standardization efforts of the PoC communications the OMA (Open Mobile Alliance) as defined that implicit activation of a SIP-SUBSCRIBE for the first PoC client units is not carried out with the SIP-INVITE message. Instead, according to the proposals of the OMA standardization the first PoC client unit can optionally transmit a SUBSCRIBE message in order to be informed of how “selected” second PoC client units have replied, that is to say whether they have rejected the call or accepted it, whether they cannot be reached or whether they are busy, etc.
FIG. 4 shows, in a further message flowchart 400, a setup, provided at the present within the scope of the OMA standardization, of a PoC communications link for the case in which the PoC server unit 203 is operated in the unconfirmed indication mode.
According to this proposal, in response to the transfer of a communications link setup request message 401 in the form of a SIP-INVITE message 401 from the first PoC client unit 201 to the PoC server unit 203 via the IMS core communications network 202 an unconfirmed enable message in the form of a SIP-UNCONFIRMED-OK message 402 is transferred from the PoC server unit 203 via the IMS core communications unit 202 to the first PoC client unit 201, and a SIP floor granted message 403 is then transmitted from the PoC server unit 203 to the first PoC client unit 201, and the channel for transmitting useful data, in particular voice data, from the first PoC client unit 201 to the PoC server unit 203 is thus enabled.
Useful data message 404 are then transmitted from the first PoC client unit 201 to the PoC server unit 203.
As shown in the message flowchart 400, it is not provided for the selection as to whether the confirmed indication mode or the unconfirmed indication mode is to be used to be left to the first PoC client unit 201.
If the PoC service unit 203 is operated in the unconfirmed indication mode, the user of the first PoC client unit 201 must always accept the unconfirmed indication mode although this may constitute a bad user experience from the point of view of the user of the first PoC client unit 201, i.e. may lead to inconvenience for the user. This is the case, for example, if the user of the first PoC client unit 201 starts to speak and transmits useful data messages 404 and does not learn until a later time that there was no possibility at all of setting up a push-to-talk communications link to a second, i.e. selected PoC client unit since, for example, all selected PoC client units either could not be reached, were busy or rejected the call.
It is thus desirable that the user of the first PoC client unit 201 should always have the choice between the two available indication modes.
According to the current proposal within the scope of OMA standardization a SUBSCRIBE the (result) message 405 is provided as an optional message which is transmitted from the first PoC client unit 201 via the IMS core communications network 202 to the PoC server unit 203, after which the PoC server unit 203 can, if appropriate, transmit a subscriber confirmation message, in the form of a SIP-NOTIFY (result) message 406, to the first PoC client unit 201 in order to indicate that the selected second PoC client unit or units have accepted or rejected the requests to set up a communications link.
Since the SUBSCRIBE message 405 and the SIP-NOTIFY (result) message 406 are provided as optional messages, this means that a user of the first PoC client unit 201 does not need to use this feature, specifically that he is informed as soon as a “selected” second PoC client unit has responded.
If a user of the first PoC client unit 201 does not use this feature, this means, however, that no SIP-NOTIFY (result) messages 406 are transferred to him, as a result of which it is no longer possible for the user of the first PoC client unit 201 to choose between the two indication modes. This results from the fact, as described above, that a SIP-NOTIFY message is necessary if the PoC server unit 203 uses the unconfirmed indication mode but the user of the first PoC client unit 201 would like to use the confirmed indication mode.